Handheld field maintenance tools are known. Such tools are highly useful in the process control and measurement industry to allow operators to conveniently communicate with and/or interrogate field devices in a given process installation. Examples of such process installations include petroleum, pharmaceutical, chemical, pulp, and other fluid processing installations. In such installations, the process control and measurement network may include tens or even hundreds of various field devices which periodically require maintenance to ensure that such devices are functioning properly and/or calibrated. Moreover, when one or more errors in the process control and measurement installation are detected, the use of a handheld field maintenance tool allows technicians to quickly diagnose such errors in the field.
Since at least some process installations may involve highly volatile, or even explosive, environments, it is often beneficial, or even required, for field devices and the handheld field maintenance tools used with such field devices to comply with intrinsic safety requirements. These requirements help ensure that compliant electrical devices will not generate a source of ignition even under fault conditions. One example of Intrinsic Safety requirements is set forth in: APPROVAL STANDARD INTRINSICALLY SAFE APPARATUS AND ASSOCIATED APPARATUS FOR USE IN CLASS I, II and III, DIVISION NUMBER 1 HAZARDOUS (CLASSIFIED) LOCATIONS, CLASS NUMBER 3610, promulgated by Factory Mutual Research October, 1998. An example of a handheld field maintenance tool that complies with intrinsic safety requirements includes that sold under trade designation Model 375 Field Communicator, available from Fisher-Rosemount Systems, Inc. of Eden Prairie, Minn.
Given the unique environmental considerations for field devices, communication signaling has traditionally been carefully controlled. Examples of industrial process communication protocols include the Highway Addressable Remote Transducer (HART®) Protocol, and the FOUNDATION™ Fieldbus Protocol.
The HART® Communication Protocol has a hybrid physical layer consisting of digital communication signals superimposed on the standard 4-20 mA analog signal. The data transmission rate is 1.2 Kbits/sec. The HART® Protocol is a de facto standard in the process industries.
Another major process industry communication protocol is known as the FOUNDATION™ Fieldbus Communication Protocol. This protocol is based on an ISA standard (ISA—S50.01-1992, promulgated by the Instrument Society of America in 1992). A practical implementation was specified by the Fieldbus Foundation (FF). FOUNDATION™ Fieldbus is an all digital communication protocol with a transmission rate of approximately 31.25 Kbits/sec.
Recently, some field devices have been designed to communicate wirelessly. These field devices, accordingly, do not require any communication or power wiring thereby simplifying field wiring, as well as interaction with the device. However, handheld field maintenance tools with terminals that are designed to physically couple to wiring terminals of a field device are simply not able to communicate with these new wireless field devices.